Thermal stability and structural characteristics of HfO₂ films on Si (100) grown by atomic-layer deposition

The thermal stability and structural characteristics for gate stack structure of HfO₂ dielectrics deposited by atomic-layer deposition (ALD) were investigated. The structural characteristics and chemical state of the HfO₂ films in relation to the film thickness and postannealing temperature were examined by x-ray diffraction and x-ray photoelectron spectroscopy. An interfacial layer of hafnium silicate with an amorphous structure was grown on the oxidized Si substrate at an initial growth stage. The structural characteristics of the HfO₂ films are closely affected by the interfacial layer and are depended on the thickness of the films. The 45 Å thick HfO₂ film with an amorphous structure was changed into a polycrystalline structure after rapid temperature annealing of 750°C for 5 min, while thicker films were grown into a polycrystalline structure of monoclinic or tetragonal crystal structure. The silicate layer grown at the interfacial region is not stable even at 700°C under ultrahigh vacuum condition and changes into the silicide layers.